The key finding is: Although charging electric vehicles at night (when electricity is cheap and wind power is typically more plentiful) could lower electricity costs, doing so also creates more air emissions, and the health and environmental costs from these emissions outweigh the electricity cost savings. The study is specific to the PJM portion of the electricity grid, to which Pittsburgh, Washington DC, and Chicago belong. More precisely, the “charging at night when electricity is cheap” idea is implemented by allowing the grid operator to throttle the charging speed of electric vehicles as needed so that they can operate the system more cost effectively. This results in greater utilization of cheap coal plants, which produce more harmful emissions.

In a future with sufficient coal plant retirement and sufficient wind power, the result could change — controlled charging could result in positive net benefits instead of negative. The result depends on the details of the region, so other parts of the US and the world could be different — but the question of electricity costs vs. health and environmental cost is important to ask everywhere.